Fiber Material Having a Manganese Oxide Coating

ABSTRACT

Various embodiments of the teachings herein include methods for coating a fiber material with manganese oxide. For example, a method may include: applying a manganese oxide precipitate to the fiber material; drying the manganese oxide precipitate; and oxidizing the manganese oxide precipitate using an oxygen plasma at a temperature below 200° C. forming a manganese(IV) oxide layer having at least 70% by weight with respect to the manganese oxide precipitate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2021/069726 filed Jul. 15, 2021, which designates the United States of America, and claims priority to EP Application No. 20188829.4 filed Jul. 31, 2020, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to fiber materials. Various embodiments of the teachings herein include methods for coating a fiber material, particularly a nonwoven, with a manganese oxide, methods for producing an antiviral and antibacterial layer, and/or fiber materials comprising manganese oxide.

BACKGROUND

Fiber materials, particularly nonwoven materials, consisting of plastics such as polypropylene fibers or polyamide fibers or else of cellulose-based materials are provided with an antibacterially or antivirally active layer for use in respiratory protection masks. For example, application DE 10 2020 203 783.3 teaches a fiber material for antibacterial and/or antiviral use is produced that comprises fibers having a coating of metallic silver and manganese(IV) oxide. One constituent of this antibacterially and antivirally active layer is manganese dioxide which is precipitated by wet-chemical means inter alia onto the nonwoven from potassium permanganate and manganese (II) salts by way of a redox reaction. After drying of the MnO₂ precipitate at 110° C., there still remain hydroxyl groups (also called hydroxy groups) and water molecules in atomic layer thickness on the MnO₂ surface, and these can influence the antibacterial and antiviral effect of the layer. It should be noted that, after a heat treatment at 110° C., the resulting manganese oxide precipitate consists of approx.:

-   60% manganese(IV) oxide - MnO₂, -   25% manganese(III) oxide - Mn₂O₃ and -   15% manganese(II) oxide - MnO.

The proportion of manganese(IV) oxide can be increased to 80% by means of an annealing process at above 400° C. in the presence of oxygen. These high temperatures are not possible particularly in the case of synthetic fiber materials, for example nonwoven materials, since these materials would be thermally damaged or even decomposed.

SUMMARY

The teachings of the present disclosure include methods that make it possible to increase the proportion of manganese(IV) oxide and to not damage the fiber material in doing so. Furthermore, the teachings of the present disclosure include a fiber material having an increased proportion of manganese(IV) oxide. For example, some embodiments include a method for coating a fiber material (10) with manganese oxide, comprising: applying a manganese oxide precipitate to the fiber material, drying the manganese oxide precipitate, and oxidizing the manganese oxide precipitate by means of an oxygen plasma at a temperature below 200° C., in particular below 160° C., so that a manganese(IV) oxide layer having at least 70% by weight with respect to the manganese oxide precipitate is formed.

In some embodiments, the manganese oxide precipitate is applied wet-chemically, in particular from potassium permanganate and manganese(II) salts.

In some embodiments, the method further comprises removing hydroxyl groups from the manganese(IV) oxide layer.

As another example, some embodiments include a method for producing an antiviral and/or antibacterial fiber material, comprising coating a fiber material (10) with manganese(IV) oxide by a method as claimed in any of the preceding claims and applying silver to the fiber material (10).

In some embodiments, the silver is applied as a silver nitrate solution and is reduced to form silver by means of a reducing agent.

In some embodiments, the method further comprises drying the fiber material under a protective gas atmosphere.

As another example, some embodiments include a fiber material (10) having a melting temperature and/or a decomposition temperature below 200° C., also having a manganese oxide coating that has at least 70% by weight, in particular at least 75% by weight, of manganese(IV) oxide, with respect to the manganese oxide coating.

In some embodiments, the manganese oxide coating has less than 5% by weight, in particular less than 1% by weight, of manganese(II) oxide with respect to the manganese oxide coating.

In some embodiments, the fiber material comprises silver.

In some embodiments, the fiber material comprises polymer fibers, particularly polypropylene fibers.

As another example, some embodiments include a mouth/nose protector comprising a fiber material as described herein.

As another example, some embodiments include an item of personal protective equipment comprising a fiber material as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present disclosure are described and explained in more detail in the text that follows on the basis of the exemplary embodiments illustrated in the FIGURE. The figure shows an example of a plant for carrying out the method incorporating teachings of the present disclosure.

DETAILED DESCRIPTION

As an example, some embodiments of the teachings herein include a method for coating the fiber material with manganese oxide including:

-   applying a manganese oxide precipitate to the fiber material, -   drying the manganese oxide precipitate, -   oxidizing the manganese oxide precipitate by means of an oxygen     plasma at a temperature below 200° C., in particular below 160° C.,     so that a manganese (IV) oxide layer having at least 70% by weight     with respect to the manganese oxide precipitate is formed.

This method is particularly gentle with respect to the fiber material and enables a significantly enlarged material selection of fibers that cannot otherwise be provided with an improved manganese oxide coating. The manganese oxide precipitate usually comprises manganese oxides in different oxidation states that are oxidized using the present method to form a manganese(IV) oxide layer of high quality. To this end, the annealing process at 400° C. or above that is known from the prior art is replaced by another energy-transferring process.

In some embodiments, the manganese oxide precipitate is applied wet-chemically, in particular from potassium permanganate and manganese(II) salts. Use may be made of a spraying process that is well suited in particular for web materials. For example, the manganese oxide precipitate may be sprayed via nozzles onto the fiber material as a potassium permanganate solution and as a manganese(II) salt solution (possible salts here are, for example, nitrate or acetate). When these two solutions come into contact with one another, a mixture of manganese oxides with different oxidation states is precipitated. The precipitate is preferably dried by means of a heating system, in particular to remove water. It has been found that 110° C. may be advantageous here.

In some embodiments, the manganese oxide precipitate is oxidized by means of an oxygen plasma. Oxidizing by means of oxygen plasma has the advantage that a high oxidation rate of the various manganese oxides to form manganese(IV) oxide is made possible in the case of comparatively low temperatures, in particular below 200° C. This further improves the properties of the fiber material. The fiber material may thus be placed into a vacuum system after the drying and treated with oxygen plasma, for example by means of a hollow cathode plasma source, in order to convert the undesired manganese oxides (particularly manganese(II) and manganese(III) oxides) into the bactericidally and virucidally active manganese dioxide (manganese(IV) oxide).

In some embodiments, the method comprises removing hydroxyl groups from the manganese(IV) oxide layer. A possible reaction equation is:

The removal of the hydroxyl groups may be carried out particularly advantageously in one step with the oxidation using oxygen plasma. The negative oxygen ions react with the manganese(II) oxide and the manganese(III) oxide to form the bactericidally active manganese (IV) oxide and at the same time the hydroxyl groups and water molecules adhering to the manganese oxide mixture are removed as steam by means of a turbopump in a vacuum chamber. Removing the hydroxyl groups and the water molecules still adhering to the manganese oxide precipitates in atomic layer thickness after direct production of said precipitates advantageously makes it possible, when depositing silver, to establish chemically closer contact between the silver and the manganese(IV) oxide.

In some embodiments, the method comprises applying silver to the fiber material that has been provided with manganese(IV) oxide by one or more of the methods incorporating teachings of the present disclosure. This step may be carried out after the manganese (IV) oxide has been applied. An antibacterial and antiviral layer having a very good effect is thus formed.

In some embodiments, the silver is applied as a silver nitrate solution and reduced to form silver by means of a reducing agent. This may be carried out by means of silver nitrate solution and hypophosphorous acid as reducing agent for the silver nitrate that are applied via nozzles.

In some embodiments, the fiber material is dried under a protective gas atmosphere. Once the silver has precipitated, the nonwoven is dried under a protective gas atmosphere (nitrogen or argon). It has been found that 110° C. may be advantageous here for the drying, also in order to remove residual water. The protective gas atmosphere may be advantageous in order that the silver is not oxidized. The order in which the bactericidal active ingredients are deposited may be advantageous in this method since, due to the risk of oxidation of the silver, the manganese (IV) oxide is applied first and then the silver. This results in improved chemical contact between the silver and the manganese oxide.

Some embodiments include a fiber material having a manganese oxide coating that has at least 70% by weight of manganese(IV) oxide with respect to the manganese oxide coating. The weight in % with respect to the manganese oxide coating is determined here without the weight of the fibers. At least 75% by weight with respect to the manganese oxide coating may be advantageous. 80% by weight or more % by weight with respect to the manganese oxide coating is also possible with one or more of the methods incorporating teachings of the present disclosure. The fiber material here has a particularly high concentration of manganese(IV) oxide.

In some embodiments, the manganese oxide coating has less than 5% by weight, in particular less than 1% by weight, of manganese(II) oxide, in each case with respect to the total weight of the manganese oxide coating. The lower the proportion of manganese(II) oxide, the higher the quality of the coating on the fiber material. It has been found that, by employing the methods described herein, the proportion of manganese(II) oxide may be reduced in particular by means of the plasma process.

In some embodiments, the fiber material has a melting temperature below 200° C. It is also possible to select fibers having a melting temperature of below 180° C. or even 160° C. This expands the material selection particularly in the case of skin-compatible nonwoven materials, for example polypropylene. Furthermore, it is also possible to process fiber materials that do not have a melting point, but rather thermally decompose. The temperature range is analogous here to the melting temperatures with decomposition temperatures below 200° C., 180° C. or even below 160° C. This fiber material may be produced using one or more of the methods described herein.

In some embodiments, the fiber material comprises silver. The fiber material comprises silver in order to achieve an improved antibacterial and antiviral effect.

In some embodiments, the fiber material may further comprise polymer fibers, particularly polypropylene fibers. The fiber material may consist completely of the polymer fibers coated with the manganese oxide layer.

As another example, some embodiments include a mouth/nose protector, comprising a fiber material incorporating teachings of the present disclosure. The fiber material may also be used in personal protective equipment.

FIG. 1 shows a plant 100 that can process a fiber material 10 and provide it with a manganese oxide coating. Possible fiber materials 10 are for example nonwovens made of polymers used in respiratory protection masks, such as polypropylene fibers or polyamide fibers. To this end, the plant 100 has a first roll 101, on which the fiber material 10 is delivered and which provides the fiber material 10 for the transport through the plant 100. Furthermore, the plant has a second roll 102, on which the finished fiber material is rolled up. The rolls 101, 102 may be configured as transportable transport rolls.

The plant 100 further has a first nozzle 121 that applies potassium permanganate solution to the fiber material 10 and a second nozzle 122 that applies manganese(II) salt solution or manganese(II) acetate solution to the fiber material 10. It is thus possible for a nonwoven made of plastic to be sprayed with a potassium permanganate solution and a manganese(II) salt solution via the nozzles 121, 122, where nitrate or acetate are usable as salt. A first heating system 130 dries the resultant manganese oxide precipitate, in particular at 110° C.

Fiber materials 10 made of plastic usually withstand temperatures up to at most 160° C., in special cases up to 200° C., then these plastics melt and decomposition takes place at even higher temperatures. Therefore, in the plant 100, a possible annealing process at 400° C. has been replaced by another energy-transferring process.

To this end, the plant 100 has a plasma generator 110 that provides the possibility of applying oxygen plasma 112 to the fiber material 10 provided with the dried manganese oxide precipitate. A plasma process (for example hollow cathode plasma, inductively coupled plasma, capacitively coupled plasma or microwave plasma) makes it possible to ionize oxygen molecules and oxygen atoms. This produces atomic oxygen and oxygen ions O⁻, O₂ ⁻, O₃ ⁻ that react with the manganese oxide surface produced shortly beforehand in the plant and this is oxidized to the corresponding manganese(IV) oxide.

In some embodiments, there is a hollow cathode plasma source in plasma generator 110, because the hollow cathode, due to its shape, can trap oxygen ions and electrons in its cavities and thus ensures high plasma density (electron density). Furthermore, the voltage falls after the plasma is ignited, but a further increase in the current intensity does not produce a relatively great increase in the voltage. In contrast, the voltage rises continuously with the current in the case of capacitively or inductively coupled plasma sources. This high voltage potential accelerates the ions, which receive such a high energy excess that the substrate surface can be damaged. The plasma potential remains low in the case of the hollow cathode, with the result that the ions receive less energy and do not damage the substrate surface.

The fiber material 10, for example a polymer nonwoven, that is coated with the manganese oxide precipitate (a mixture of manganese oxides in various oxidation states of the manganese) may be introduced into a vacuum chamber. In order to convert manganese 2+ and manganese 3+ into a higher oxidation state, oxygen is introduced into a hollow cathode plasma source.

In this plasma generator 110 configured as a hollow cathode plasma source, high voltage (100 to 300 volts) is generated between anode and cathode by means of a radiofrequency plasma generator and impedance differences (AC resistances) occurring here are minimized and matched in a matching box. The oxygen molecules can be ionized at 12.06 eV and the oxygen atom can be ionized at 13.62 eV. The discharge of the oxygen molecules is performed mainly by direct electron impact dissociation and by dissociative electron addition. Unstable excited O₂ ⁻* are formed as intermediates, which then break up into atomic oxygen and oxygen ions. Oxygen discharges are weakly negative, meaning that a fraction of the negative charge consists of ions instead of electrons. The negative ions are O⁻, O₂ ⁻ and even O₃ ⁻. These negative oxygen ions react with the manganese(II) oxide and the manganese(III) oxide to form the bactericidally active manganese(IV) oxide and at the same time the hydroxyl groups and water molecules adhering to the manganese oxide mixture are removed as steam. This can be carried out by a turbopump 114 in a vacuum chamber. Nonwovens consisting predominately of polymers and cellulose-based materials can thus easily be coated in a roll-to-roll process.

Subsequently, a silver nitrate solution, via a third nozzle 123, and a reducing agent for the silver nitrate (for example hypophosphorous acid), via a fourth nozzle 124, are sprayed onto the fiber material 10 coated/endowed with manganese(IV) oxide. Once the silver has been precipitated, the fiber material 10 is dried in a second heating system 140 preferably under a protective gas atmosphere (nitrogen or argon) at preferably 110° C. This drying removes excess water. The protective gas atmosphere is advantageous in order that the silver is not oxidized. The order in which the bactericidal active ingredients are deposited is also advantageous in this method. Due to the risk of oxidation of the silver, the method may include first applying the manganese(IV) oxide, then the silver. The nonwoven can be moved automatically by means of the transport rolls 101, 102. The plant 100 can be controlled in a computer-assisted manner by means of an electronic controller.

In summary, the teachings herein include methods for coating a fiber material (10), particularly a nonwoven, with a manganese oxide, to a method for producing an antiviral and antibacterial layer, and to a fiber material comprising manganese oxide. In order to increase the proportion of manganese(IV) oxide on the fiber material (10), the following steps are proposed:

-   applying a manganese oxide precipitate to the fiber material, -   drying the manganese oxide precipitate, -   oxidizing the manganese oxide precipitate at a temperature below     200° C., in particular below 160° C., so that a manganese(IV) oxide     layer having at least 70% by weight with respect to the manganese     oxide precipitate is formed.

Reference symbols 10 fiber material 100 plant 101 first roll 102 second roll 110 plasma source 112 plasma 114 turbopump 121 first nozzle 122 second nozzle 123 third nozzle 124 fourth nozzle 130 first heating system 140 second heating system 

What is claimed is:
 1. A method for coating a fiber material with manganese oxide, the method comprising: applying a manganese oxide precipitate to the fiber material; drying the manganese oxide precipitate; and oxidizing the manganese oxide precipitate using an oxygen plasma at a temperature below 200° C. forming a manganese (IV) oxide layer having at least 70% by weight with respect to the manganese oxide precipitate.
 2. The method as claimed in claim 1, further comprising applying the manganese oxide precipitate wet-chemically from potassium permanganate and manganese(II) salts.
 3. The method as claimed in claim 1, further comprising removing hydroxyl groups from the manganese(IV) oxide layer.
 4. A method for producing an antiviral and/or antibacterial fiber material, the method comprising: applying a menganese ozide precipitate to the fiber material; drying the manganese oxide precipitate; oxidizing the manganese oxide precipitate using an oxygen plasma at a temperature below 200° C. forming a manganese(IV) oxide layer having at least 70% by weight with respect to the manganese oxide precipitate; and applying silver to the fiber material.
 5. The method as claimed in claim 4, wherein applying silver comprises: applying a silver nitrate solution; and reducing the silver nitrate solution to form silver using a reducing agent.
 6. The method as claimed in claim 4, further comprising drying the fiber material under a protective gas atmosphere.
 7. A fiber material having a melting temperature and/or a decomposition temperature below 200° C., also having a manganese oxide coating that has at least 70% by weight, in particular at least 75% by weight, of manganese(IV) oxide, with respect to the manganese oxide coating.
 8. The fiber material as claimed in claim 7, wherein the manganese oxide coating has less than 5% by weight of manganese(II) oxide with respect to the manganese oxide coating.
 9. The fiber material as claimed in claim 7, further comprising silver.
 10. The fiber material as claimed in claim 7, further comprising polymer fibers. 11-12. (canceled) 